This invention relates to a method and apparatus for transmitting emergency loads and is applicable to automotive seat tracks. The invention provides a method and apparatus for automotive seat track construction. More specifically, the method and apparatus of the invention is applicable to the transmission of loads in automobile seat tracks under emergency conditions in which, for example following a vehicle impact, there is a requirement for the track to transmit the maximum load which it must be capable of transmitting. Under such conditions, the seat track is designed to deform in a specific manner, that is to say the design is such that the relevant part of the seat track assembly deforms in a predetermined manner.
For this purpose, the seat track design is such that defined parts must not deform (ie must have sufficient strength) before other elements of the seat track design. This includes parts of the seat track which, by virtue of their inherent shape or geometry or mechanical relationship with other components, are subjected to significantly greater stresses than other parts. For example, it may be necessary for certain parts of a basically two-part sliding seat track assembly to resist bending under emergency conditions up to a predetermined load.
We have determined that the particular load requirements of automotive seat tracks, which include a relatively complex intermix of bending and tension forces, is susceptible to a design approach (as defined in the claims hereto) whereby the relatively high bending strength requirements are related to the corresponding tension-resisting requirements in such a way that an integrated design structure is obtained which is capable of meeting the design requirements in respect of overall strength to meet overload conditions in an improved manner with respect to currently available designs, and an object of the present invention is provide improvements in one or more of these respects, or indeed improvements generally.
There is disclosed in GB-A-2,282,551 (Mercedes-Benz) a process for producing a metal sheet which may be used in the fabrication of motor vehicle bodies and which sheet is stepped in cross-section. The method utilises an extruded profile having differing wall thicknesses which is rolled from the hollow circular profile shown in FIG. 3 to produce after cutting, the profiles shown in FIGS. 1 and 2.
There is disclosed in U.S. Pat. No. 5,338,119 (Hammerstein GmbH) a seat slide for vehicle seats in which the tracks are manufactured of steel sheet containing at least 0.35% carbon content and which are heat treated after completion. The tracks have a substantially higher fundamental strength than otherwise so that less material and thus lower weight can be achieved.
There is disclosed in CA-A-2,172,876 (Stampfl) a method of manufacturing a c-shaped rail by a rolling technique in which the outward migration of material during the rolling operation is offset by a subsequent rolling step using calibrating discs to return the marginal sections to their original thickness.